Riverhead Town police said Ms. Tfelt was hit by a 2000 Cadillac Deville sedan that jumped the curb and crashed into a retaining wall after striking the woman.

The driver of the Cadillac and a passenger in the car ditched the car and both ran from the scene headed south on Woodcrest Avenue, according to a police statement.

Police found Ms. Tfelt lying unconscious in the eastbound lanes of Route 58. She was rushed to Peconic Bay Medical Center, but was pronounced dead, police said.

Police closed the road in both directions between Osborn and Harrison Avenues as Riverhead and state police K-9 teams and a Suffolk County police helicopter searched the area.

The Cadillac involved in the crash was reported stolen about half an hour after the accident, police said.

Investigators believe they know the names of the two men who fled the scene, and that it’s just a matter of time before they’re tracked down, police sources said.

Ms. Tfelt, a Selden native and Newfield High School graduate, met Mr. Reiter, originally of Cutchogue, as the were both trying to recover from drug addiction in 2010, and the couple had been together ever since, he said.

The couple had a child in December 2011 — a boy named Joseph Reiter III. After the baby was born, Mr. Reiter worked to support the family while Ms. Tfelt cared for the child.

“She took care of that baby every single day by herself,” he said. “She’s an amazing mother.”

Mr. Reiter said Ms. Tfelt had her share of struggles with addiction, but added that she had worked through rehab and was trying to recover.

“She’s a beautiful girl,” he said. “She was looking good … She started her life all over again.”

Mr. Reiter said the family hasn’t yet made funeral arrangements.

Anyone with information about the crash is asked to call Riverhead police at (631) 727-4500, ext. 326. All call will be kept confidential.